Atomic layer etching using a boron-containing gas and hydrogen fluoride gas

ABSTRACT

Embodiments of the invention provide a method for atomic layer etching (ALE) of a substrate. According to one embodiment, the method includes providing a substrate, and exposing the substrate to hydrogen fluoride (HF) gas and a boron-containing gas to etch the substrate. According to another embodiment, the method includes providing a substrate containing a metal oxide film, exposing the substrate to HF gas to form a fluorinated surface layer on the metal oxide film, and exposing the substrate to a boron-containing gas to remove the fluorinated surface layer from the metal oxide film. The exposures may be repeated at least once to further etch the metal oxide film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority to U.S. ProvisionalPatent Application Ser. No. 62/373,232 filed on Aug. 10, 2016, theentire contents of which are herein incorporated by reference.

FIELD OF INVENTION

The present invention relates to the field of semiconductormanufacturing and semiconductor devices, and more particularly, toatomic layer etching (ALE) of a substrate using a boron-containing gasand hydrogen fluoride (HF) gas.

BACKGROUND OF THE INVENTION

As device feature size continues to scale it is becoming a significantchallenge to accurately control etching of fine features. For highlyscaled nodes 10 nm and below, devices require atomic scaled fidelity orvery tight process variability. There is significant impact on deviceperformance due to variability. In this regards, self-limiting andatomic scale processing methods such as ALE are becoming a necessity.

SUMMARY OF THE INVENTION

A method is provided for ALE of a substrate. According to oneembodiment, the method includes providing a substrate, and exposing thesubstrate to HF gas and a boron-containing gas to etch the substrate.

According to another embodiment, the method includes providing asubstrate containing a metal oxide film, exposing the substrate to HFgas to form a fluorinated surface layer on the metal oxide film, andexposing the substrate to a boron-containing gas to remove thefluorinated surface layer from the metal oxide film. The exposures maybe repeated at least once to further etch the metal oxide film.

According to yet another embodiment, the method includes providing asubstrate containing a metal oxide film having a first fluorinatedsurface layer, exposing the substrate to a first boron-containing gas toremove the first fluorinated surface layer from the metal oxide film,exposing the substrate to HF gas to form a second fluorinated surfacelayer on the metal oxide film, and exposing the substrate to a secondboron-containing gas to remove the second fluorinated surface layer fromthe metal oxide film. The exposures to the HF gas and the secondboron-containing gas may be repeated at least once to further etch themetal oxide film.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a process flow diagram for processing a substrate according toan embodiment of the invention;

FIG. 2 is a process flow diagram for processing a substrate according toan embodiment of the invention;

FIGS. 3A-3D schematically show through cross-sectional views a method ofprocessing a substrate according to an embodiment of the invention;

FIG. 4 is a process flow diagram for processing a substrate according toan embodiment of the invention;

FIGS. 5A-5F schematically show through cross-sectional views a method ofprocessing a substrate according to an embodiment of the invention;

FIG. 6 is a process flow diagram for processing a substrate according toan embodiment of the invention; and

FIG. 7 is a process flow diagram for processing a substrate according toan embodiment of the invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

Developing advanced technology for advanced semiconductor technologynodes presents an unprecedented challenge for manufacturers ofsemiconductor devices, where these devices will require atomic-scalemanufacturing control of etch variability. ALE is viewed by thesemiconductor industry as an alternative to conventional continuousetching. ALE is a substrate processing technique that removes thinlayers of material using sequential self-limiting reactions and isconsidered one of the most promising techniques for achieving therequired control of etch variability necessary in the atomic-scale era.

ALE is often defined as a film etching technique that uses sequentialself-limiting reactions. The concept is analogous to atomic layerdeposition (ALD), except that removal occurs in place of a secondadsorption step, resulting in layer-by-layer material removal instead ofaddition. The simplest ALE implementation consists of two sequentialsteps: surface modification (1) and removal (2). Surface modificationforms a thin reactive surface layer with a well-defined thickness thatis subsequently more easily removed than the unmodified material. Thethin reactive surface layer is characterized by a sharp gradient inchemical composition and/or physical structure of the outermost layer ofa material. The removal step takes away at least a portion of the thinreactive surface layer while keeping the underlying substrate intact,thus “resetting” the surface to a suitable state for the next etchingcycle. The total amount of material removed is determined by the numberof repeated cycles.

Embodiments of the invention provide a method for manufacturing ofsemiconductor devices, and more particularly, to ALE using HF gas and aboron-containing gas. FIG. 1 is a process flow diagram for processing asubstrate according to an embodiment of the invention. The process flow1 includes, in 100, providing a substrate, and in 102, exposing thesubstrate to HF gas and a boron-containing gas to etch the substrate.The exposures may be alternating or may have some temporal overlap andmay be repeated at least once to further etch the substrate. Theboron-containing gas can contain a boron hydride, a boron halide, aboron amide, an organo boride, or a combination thereof. Theboron-containing gas may be selected from the group consisting of BH₃,BCl₃, B(CH₃)₃, and B(N(CH₃)₂)₃. According to one embodiment, thesubstrate contains a metal oxide film that is etched by the gasexposures. The metal oxide film may be selected from the groupconsisting of Al₂O₃, HfO₂, TiO₂, ZrO₂, Y₂O₃, La₂O₃, UO₂, Lu₂O₃, Ta₂O₅,Nb₂O₅, ZnO, MgO, CaO, BeO, V₂O₅, FeO, FeO₂, CrO, Cr₂O₃, CrO₂, MnO,Mn₂O₃, RuO, CoO, WO₃, and combinations thereof.

FIG. 2 is a process flow diagram for processing a substrate according toan embodiment of the invention. Referring also to FIGS. 3A-3D, theprocess flow 2 includes, in 200, providing a substrate 3 containing ametal oxide film 302 on a layer 300. For example, the metal oxide film302 may be selected from the group consisting of Al₂O₃, HfO₂, TiO₂,ZrO₂, Y₂O₃, La₂O₃, UO₂, Lu₂O₃, Ta₂O₅, Nb₂O₅, ZnO, MgO, CaO, BeO, V₂O₅,FeO, FeO₂, CrO, Cr₂O₃, CrO₂, MnO, Mn₂O₃, RuO, CoO, WO₃, and combinationsthereof. In 202, the substrate 3 is exposed to HF gas 306 to form afluorinated surface layer 304 on the metal oxide film 302. In 204, thesubstrate 3 may be purged with an inert gas (e.g., argon (Ar) ornitrogen (N₂)) to remove excess HF and reaction byproducts. In 206, thesubstrate 3 is exposed to a boron-containing gas 308 to react with andremove the fluorinated surface layer 304. The reaction byproductsinclude volatile BF₃ species and metal-containing species that desorbfrom the substrate 3 and are efficiently pumped out of the processchamber. The inventors have discovered that the use of theboron-containing gas 308 in combination with fluorinated surface speciesadvantageously allows for low-temperature thermal ALE in the absence ofa plasma. The boron-containing gas 308 can contain a boron hydride, aboron halide, a boron amide, an organo boride, or a combination thereof.The boron-containing gas 308 may be selected from the group consistingof BH₃, BCl₃, B(CH₃)₃, and B(N(CH₃)₂)₃. In 208, the substrate 3 may bepurged with an inert gas to remove excess boron-containing gas andreaction byproducts. As shown by process arrow 210, the alternatingexposures 202-208 may be repeated at least once to further etch themetal oxide film 302. The alternating exposures 202-208 constitute oneALE cycle.

FIG. 4 is a process flow diagram for processing a substrate according toan embodiment of the invention. Referring also to FIGS. 5A-5F, theprocess flow 4 includes, in 400, providing a substrate 5 containing ametal oxide film 502 having a first fluorinated surface layer 504. Forexample, the metal oxide film 502 may be selected from the groupconsisting of Al₂O₃, HfO₂, TiO₂, ZrO₂, Y₂O₃, La₂O₃, UO₂, Lu₂O₃, Ta₂O₅,Nb₂O₅, ZnO, MgO, CaO, BeO, V₂O₅, FeO, FeO₂, CrO, Cr₂O₃, CrO₂, MnO,Mn₂O₃, RuO, CoO, WO₃, and combinations thereof. The first fluorinatedsurface layer 504 may be formed by wet processing (e.g., using aqueousHF) or by dry processing (e.g., using HF gas). In one example, the firstfluorinated surface layer 504 may be formed by an etching process thatutilizes an organic fluorine-containing etching gas. In 402, thesubstrate 5 is exposed to a first boron-containing gas 506 to remove thefirst fluorinated surface layer 504 from the metal oxide film 502. In404, the substrate 5 may be purged with an inert gas to remove excessfirst boron-containing gas and reaction byproducts. In 406, thesubstrate 5 is exposed to HF gas 508 to form a second fluorinatedsurface layer 510 on the metal oxide film 502. In 408, the substrate 5may be purged with an inert gas to remove excess HF gas and reactionbyproducts. In 410, the substrate 5 is exposed to a secondboron-containing gas 512 to remove the second fluorinated surface layer510 from the metal oxide film 502.

The first and second boron-containing gases 506 and 512 can contain aboron hydride, a boron halide, a boron amide, an organo boride, or acombination thereof. The first and second boron-containing gases 506 and512 may independently be selected from the group consisting of BH₃,BCl₃, B(CH₃)₃, and B(N(CH₃)₂)₃. As shown by process arrow 412, theexposures 404-410 may be repeated at least once to further etch themetal oxide film 502.

FIG. 6 is a process flow diagram for processing a substrate according toan embodiment of the invention. The process flow illustrates the halfreactions and the overall reaction for exemplary ALE of Al₂O₃ usingalternating exposures of HF gas and BH₃ gas. The reaction byproductsinclude volatile BF₃ species, AlH₃ species and H₂O species that desorbfrom the substrate and are efficiently pumped out of the processchamber.

FIG. 7 is a process flow diagram for processing a substrate according toan embodiment of the invention. The process flow illustrates the halfreactions and the overall reaction for exemplary ALE of Al₂O₃ usingalternating exposures of HF gas and BL₃ gas, where L can includehydrogen, a halogen, an amide, or an organic group. Examples of BL₃include BH₃, BCl₃, B(CH₃)₃, and B(N(CH₃)₂)₃. The reaction byproductsinclude volatile BF₃ species, AlL₃ species and H₂O species that desorbfrom the substrate and are efficiently pumped out of the processchamber.

A plurality of embodiments for atomic layer etching using aboron-containing gas and HF gas have been described. The foregoingdescription of the embodiments of the invention has been presented forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.This description and the claims following include terms that are usedfor descriptive purposes only and are not to be construed as limiting.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the aboveteaching. It is therefore intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

What is claimed is:
 1. A method of atomic layer etching (ALE), themethod comprising: providing a substrate containing a metal oxide filmhaving a first fluorinated surface layer; exposing the substrate to afirst boron-containing gas to remove the first fluorinated surface layerfrom the metal oxide film; exposing the substrate to hydrogen fluoride(HF) gas to form a second fluorinated surface layer on the metal oxidefilm; and exposing the substrate to a second boron-containing gas toremove the second fluorinated surface layer from the metal oxide film.2. The method of claim 1, wherein the exposures to the HF gas and thesecond boron-containing gas are repeated at least once to further etchthe metal oxide film.
 3. The method of claim 1, wherein the metal oxidefilm is selected from the group consisting of Al₂O₃, HfO₂, TiO₂, ZrO₂,Y₂O₃, La₂O₃, UO₂, Lu₂O₃, Ta₂O₅, Nb₂O₅, ZnO, MgO, CaO, BeO, V₂O₅, FeO,FeO₂, CrO, Cr₂O₃, CrO₂, MnO, Mn₂O₃, RuO, CoO, WO₃, and combinationsthereof.
 4. The method of claim 1, wherein the metal oxide film isformed by oxidizing a metal layer.
 5. The method of claim 1, furthercomprising gas purging with an inert gas between the exposing steps. 6.The method of claim 1, wherein the first fluorinated surface layer isformed using wet processing with aqueous HF.
 7. The method of claim 1,wherein the first and second boron-containing gases contain a boronhydride, a boron halide, a boron amide, an organo boride, or acombination thereof.
 8. The method of claim 7, wherein the first andsecond boron-containing gases are selected from the group consisting ofBH₃, BCl₃, B(CH₃)₃, and B(N(CH₃)₂)₃.
 9. The method of claim 1, whereinthe first fluorinated surface layer is formed by dry processing.
 10. Themethod of claim 9, wherein the dry processing includes HF gas or anorganic fluorine-containing etching gas.
 11. The method of claim 1,wherein the first and second boron-containing gases contain a boronhydride, a boron amide, an organo boride, or a combination thereof. 12.The method of claim 11, wherein the first and second boron-containinggases are selected from the group consisting of BH₃, B(CH₃)₃, andB(N(CH₃)₂)₃.